Methods for producing optoelectronic semiconductor components, and optoelectronic semiconductor lasers

ABSTRACT

A method for producing an optoelectronic semiconductor component includes:
         epitaxially growing a semiconductor layer sequence including an active layer on a growth substrate,   shaping a front facet at the semiconductor layer sequence and the growth substrate,   coating a part of the front facet with a light blocking layer for radiation generated in the finished semiconductor component,   wherein the light blocking layer is produced by a directional coating method and the light blocking layer is structured during coating by shading by the growth substrate and/or by at least one dummy bar arranged at and/or alongside the growth substrate.

RELATED APPLICATIONS

This application claims priority of German Patent Application No. 102011 054 954.4, filed Oct. 31, 2011, and U.S. Provisional ApplicationNo. 61/590,375, filed Jan. 25, 2012, the subject matter of which ishereby incorporated by reference.

TECHNICAL FIELD

This disclosure relates to methods for producing optoelectronicsemiconductor components and optoelectronic semiconductor lasers.

BACKGROUND

There is a need for an optoelectronic semiconductor laser wherein asubstrate mode is suppressed.

SUMMARY

We provide a method of producing an optoelectronic semiconductorcomponent including epitaxially growing a semiconductor layer sequenceincluding at least one active layer on a growth substrate, shaping afront facet at the semiconductor layer sequence and the growthsubstrate, wherein the front facet is a main light exit side forradiation generated in the semiconductor component, coating a part ofthe front facet with a light blocking layer for the radiation generatedin the semiconductor component, wherein the light blocking layer isproduced by a directional coating method and the light blocking layer isstructured during coating by shading by the growth substrate and/or byat least one dummy bar arranged at and/or alongside the growthsubstrate.

We also provide an optoelectronic semiconductor laser including a growthsubstrate, a semiconductor layer sequence that generates laserradiation, a front facet at the growth substrate and at thesemiconductor layer sequence which constitutes a main light exit sidefor the laser radiation generated in the semiconductor laser and has alight exit region at the semiconductor layer sequence, and a lightblocking layer for the laser radiation, which partly covers at least thegrowth substrate at the front facet such that the light exit region isnot covered by the light blocking layer.

We further provide a light blocking layer for an optoelectronicsemiconductor laser having an emission wavelength λ, including at leastone first and at least one second partial layer, wherein the first andsecond partial layers alternately succeed one another, two adjacentpartial layers, with a tolerance of at most λ/7, have an opticalthickness of λ/2, the second partial layers include a material absorbentfor the emission wavelength λ, the first partial layers include amaterial transmissive for the emission wavelength λ, and the lightblocking layer includes a total of 2 to 20 of the partial layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective schematic illustration of an example of anoptoelectronic semiconductor laser.

FIGS. 2A and 2B show planar views of the front facet of examples of asemiconductor laser.

FIGS. 3-6 show schematic perspective views of selected portions ofmethods of producing a semiconductor component.

FIGS. 7 and 8 show images of radiation emissions of conventionalsemiconductor lasers.

FIG. 9 shows schematic front elevational views of dummy bars.

FIG. 10A shows a perspective schematic illustration of a light blockinglayer.

FIG. 10B is a graph of Transmission plotted against wave length λ for alight blocking layer.

FIG. 10C shows a graph of Transmission T against the number N of mirrorpairs.

FIG. 11 shows a schematic side view of an example of semiconductorlaser.

FIG. 12 schematically illustrates a light blocking layer and a highlyreflective layer fitted at a rear side of an example of anoptoelectronic semiconductor laser.

FIGS. 13 and 14 are yet another example of optoelectronic semiconductorlaser.

FIGS. 15A-15E schematically illustrate selected steps of a productionmethod, in sequence, of an optoelectronic semiconductor component.

DETAILED DESCRIPTION

It will be appreciated that the following description is intended torefer to specific examples of structure selected for illustration in thedrawings and is not intended to define or limit the disclosure, otherthan in the appended claims.

We provide methods that may comprise the step of growing a semiconductorlayer sequence comprising at least one active layer on a growthsubstrate. The growth substrate can be a transparent,radiation-transmissive substrate such as a GaN substrate. Thesemiconductor layer sequence is grown epitaxially, for example, by metalorganic vapor phase epitaxy, MOVPE for short.

The semiconductor layer sequence is preferably based on a III-V compoundsemiconductor material. The semiconductor material is, for example, anitride compound semiconductor material such as Al_(n)In_(1-n-m)Ga_(m)Nor a phosphide compound semiconductor material such asAl_(n)In_(1-n-m)Ga_(m)P or an arsenide compound semiconductor materialsuch as Al_(n)In_(1-n-m)Ga_(m)As, wherein in each case 0≦n≦1, 0≦m≦1 andn+m≦1. The semiconductor layer sequence can comprise dopants andadditional constituents. For the sake of simplicity, however, only theessential constituents for the crystal lattice of the semiconductorlayer sequence, that is to say Al, As, Ga, In, N or P, are specified,even if they can be replaced and/or supplemented in part by smallamounts of further substances.

The semiconductor layer sequence comprises at least one active layerdesigned to generate an electromagnetic radiation. The active layercomprises, in particular, at least one pn junction or, preferably, oneor more quantum well structures. Radiation generated by the active layerduring operation is, in particular, in the spectral range of 380 nm to550 nm or 420 nm to 540 nm.

A front facet may be shaped at the semiconductor layer sequence and atthe growth substrate. Shaping the front facet is preferably effectedafter epitaxially growing the semiconductor layer sequence. The facet isproduced, in particular, by virtue of the fact that the growth substrateon which the semiconductor layer sequence is applied is split up, forexample, by cleavage. It is likewise possible for the facet to beproduced by etching. A projection can then be formed at the growthsubstrate and/or at the semiconductor layer sequence.

The front facet may be designed as a main light exit side for radiationgenerated in the finished semiconductor component. By way of example,the front facet is designed as the sole side to provide radiation fromthe optoelectronic semiconductor component for a selected application.The front facet is preferably a smooth, planar area. An averageroughness of the front facet is, for example, at most 100 nm or at most50 nm.

The method may comprise the step of coating a part of the front facetwith a light blocking layer. The light blocking layer is designed toblock a part of the radiation generated in the finished semiconductorcomponent. In other words, the light blocking layer is opaque to atleast one part of the radiation generated in the active layer in thesemiconductor layer sequence. A transmission for radiation generated inthe active layer through the light blocking layer is preferably at most80% or at most 10% or at most 1% or at most 0.2%. It is possible for thelight blocking layer to be completely opaque to the radiation generatedin the active layer during the operation of the semiconductor component.

The light blocking layer may be produced by a directional coatingmethod. Directional means that a material from which the light blockinglayer is shaped is applied to the front facet from a specific directionor a narrowly defined direction range. The coating method is, forexample, molecular beam epitaxy, MBE for short, or vapor deposition. Thecoating method can likewise be realized by ion beam deposition, or IBDfor short, or by sputtering.

In contrast thereto, non-directional coating methods are those in whicha coating with a material is effected independently of an orientation ofareas to be coated. Such coating methods in which no or only acomparatively low directional selectivity occurs are, for example, CVD,MOVPE or atomic layer deposition, ALD for short.

The light blocking layer may be applied in a structured fashion. That isto say that the light blocking layer does not completely cover the frontfacet and a part of the light exit side is deliberately not coated withthe light blocking layer.

The light blocking layer may be structured by shading. Shading can meanthat, as seen from a coating direction, the complete front facet is notfreely accessible.

The shading during coating with the light blocking layer may be effectedby the growth substrate on which the semiconductor layer sequence isgrown. It is likewise possible for the shading to be effected by a dummybar arranged at and/or alongside the growth substrate. No semiconductorlayer sequence comprising the active layer is then deposited on thedummy bar. In particular, no optoelectronic semiconductor component isproduced from the dummy bar.

The method may be designed to produce an optoelectronic semiconductorcomponent and comprises at least the following steps, preferably in theorder indicated:

-   -   epitaxially growing a semiconductor layer sequence comprising at        least one active layer on a growth substrate,    -   shaping a front facet at the semiconductor layer sequence and at        the growth substrate, wherein the front facet is preferably        designed as a main light exit side for radiation generated in        the finished semiconductor component,    -   coating a part of the front facet with a light blocking layer        for the radiation generated in the finished semiconductor        component, and completing the semiconductor component.

In this case, the light blocking layer is produced by a directionalcoating method and the light blocking layer is structured during coatingby shading by the growth substrate and/or by at least one dummy bararranged at and/or alongside the growth substrate.

The optoelectronic semiconductor component produced may be asemiconductor laser. The semiconductor component is then designed toemit laser radiation. In particular, the semiconductor laser is an edgeemitting laser, preferably a so-called “ridge” laser.

In the case of semiconductor lasers whose carrier substrate or growthsubstrate is transparent to a laser radiation, spontaneously emittedlight or else stray light can propagate alongside the actual laser modein the substrate. In the case of laser radiation in the visible spectralrange, the substrate therefore then itself appears luminous. Thisradiation guided in the substrate can emerge at the front facet of thesemiconductor laser and thereby reduces beam quality since the radiationno longer emerges from a single point-like region at the front facet.

Particularly if the semiconductor laser is used for laser projection byflying spot technology, this luminous emission of the substrate itselfcan lead to undesirable imaging aberrations in a projected image. By wayof example, during projection a disturbing, so-called “halo” can arisearound the actual image. In other applications, too, which require agood beam quality or a point light source, for example, in data storage,a luminous substrate is undesirable.

By applying the light blocking layer in places at the front facet, theemergence of radiation guided undesirably in the substrate can beprevented or greatly reduced. A quality of the radiation emitted by thesemiconductor laser is thereby increased.

This applies, in particular, if a semipolar GaN substrate is used as agrowth substrate for lasers emitting in the UV or emitting in the blueor in the green spectral range or if an AlGaN-free laser is involved. Inthe case of such lasers, distinct cladding layers are dispensed with andbeam guiding in the component is effected, for example, substantiallyonly via InGaN layers. Substrate modes can be particularly pronounced.

The coating with the light blocking layer may be effected while aplurality of the growth substrates with the semiconductor layersequences are assembled in a rack. That means that a plurality of thegrowth substrates and/or a plurality of the dummy bars are arrangedclosely adjacent, wherein the front facets of the growth substrates withthe semiconductor layer sequences preferably all face in the samedirection. In this case, the front facets are formed, in particular, byend sides of the growth substrates with the semiconductor layersequences.

No dummy bar may be situated between at least two adjacent growthsubstrates. In particular, a dummy bar may be situated between noadjacent growth substrates. That is to say that the growth substrateswith the semiconductor layer sequences can be arranged directly adjacentin the rack.

The front facets may be arranged parallel to one another during coatingwith the light blocking layer and therefore face in the same direction.Furthermore, the front facets, in a direction perpendicular to one ofthe front facets, are arranged offset with respect to one another. Inother words, the rack with the growth substrates then appears, as seenin side view, sawtooth-like at the front facets.

A dummy bar may be situated between at least two of the growthsubstrates with the semiconductor layer sequences. Preferably, the dummybars and growth substrates with the semiconductor layer sequencessucceed one another alternately and in an alternating fashion.

The dummy bars may project beyond the front facet during coating withthe light blocking layer. In other words, it is then possible that atone side or, preferably, at both sides of the front facet, as seen inside view, dummy bars are situated and end sides of the dummy barsproject from the rack, relative to the front facets.

A coating direction during coating of the light blocking layer may beoriented obliquely with respect to the front facets. That is to say thatthe coating direction may have an angle not equal to 90° with respect tothe front facets. As a result, it is possible that, during coating withthe light blocking layer, shading is effected by the dummy bars or byadjacent growth substrates.

At least one of the dummy bars or all of the dummy bars which areprovided for shading may have a projection. The projection preferablyextends in a direction parallel to the end sides of the dummy bars. Asseen in a plan view of the front facet, the latter is partly covered bythe projection. The projection serves as shading during coating with thelight blocking layer. It is possible that the projection is not indirect physical contact with the growth substrate and/or with thesemiconductor layer sequence.

The front facet, as seen in a plan view perpendicularly with respect tothe front facet, during coating with the light blocking layer, is notcovered by the growth substrate and/or the dummy bar. That is to saythat, as seen in a direction perpendicularly with respect to the frontfacet, the complete front facet is then freely accessible.

The light blocking layer may be applied in a structured fashion by theshading along a lateral direction. In this case, the lateral directionis oriented perpendicularly to a growth direction of the semiconductorlayer sequence and preferably also perpendicularly to a normal to thefront facets. In other words, the light blocking layer is thenstructured two-dimensionally. A part of the light blocking layer canthen be applied in at least one region laterally alongside a light exitregion.

The light exit region is, in particular, that region at the front facetin which the laser radiation intentionally leaves the semiconductorlaser and/or the semiconductor layer sequence and the growth substrate,for example, a region in which a fundamental mode of the laser radiationreaches the front facet. The light exit region is formed, in particular,by a partial region of the semiconductor layer sequence and/or by apartial region of the growth substrate near the semiconductor layersequence.

Furthermore, we provide optoelectronic semiconductor lasers. By way ofexample, the semiconductor lasers are produced by methods as describedin conjunction with one or more of the examples mentioned above.Therefore, features of the methods are also disclosed for thesemiconductor lasers, and vice versa.

The semiconductor laser may comprise a growth substrate and asemiconductor layer sequence to generate a laser radiation, wherein thesemiconductor layer sequence is produced on the growth substrate. Afront facet at the growth substrate and at the semiconductor layersequence is designed as a main light exit side for the laser radiationgenerated in the semiconductor laser during operation and has a lightexit region. A light blocking layer for the laser radiation is appliedto the front facet only in places. The light blocking layer covers thegrowth substrate only in places. The light exit region is not covered bythe light blocking layer.

Alternatively, it is possible for the growth substrate to be replaced bya carrier substrate which is different than the growth substrate.

The light blocking layer may be formed by first and second partiallayers or comprise such partial layers, wherein the partial layersalternately succeed one another. The partial layers preferably havedifferent optical refractive indexes for the laser radiation.Alternatively or additionally, it is possible for at least the firstpartial layers or at least the second partial layers to comprise amaterial which has an absorbing effect for the laser radiation having awavelength λ.

In the semiconductor laser, a layer pair, consisting of one of the firstand one of the second partial layers, may have a thickness of λ/2,preferably with a tolerance of at most λ/7 or of at most λ/10. In thiscase, the wavelength λ denotes the wavelength of the highest intensity,the so-called “peak” wavelength. It is possible for the partial layerseach to have a thickness of λ/4, with a tolerance of at most λ/7 orλ/10. The thickness of the partial layers in this case respectivelydesignates the optical thickness, that is to say the product of therefractive index of a material of the corresponding partial layer forthe wavelength λ multiplied by the geometrical thickness.

The light blocking layer may comprise a total of four to 20 of thepartial layers or two to ten of the partial layers or four to ten of thepartial layers or consists of the stated number of partial layers. Inother words, the light blocking layer then comprises one to five or twoto five pairs of partial layers.

A bonding pad may be situated at a side of the semiconductor layersequence which faces away from the growth substrate. The bonding pad isformed from a metallic material, for example, and is preferably designedto make electrical contact with the semiconductor layer sequence.

The distance between the bonding pad and the light blocking layer, forexample, in a direction parallel to a growth direction of thesemiconductor layer sequence, is at least 0.1 μm or at least 0.5 μm orat least 1 μm or at least 2 μm. Alternatively or additionally, thedistance is at most 100 μm or at most 50 μm or at most 20 μm or at most10 μm.

The light blocking layer may be shaped as a dielectric mirror, alsoknown as a Bragg mirror. The light blocking layer then comprisesalternating layers composed of a material having a high refractive indexand a low refractive index, wherein the layers preferably each have anoptical thickness of approximately λ/4 or wherein two adjacent layershave a thickness of approximately λ/2, wherein the optical thicknessesof adjacent layers can then deviate from one another by up to a factorof 3 or by up to a factor of 2 or by up to a factor of 1.25. By way ofexample, the mirror comprises 6 to 60 or 8 to 30 or 16 to 30 layers.Materials for the layers of the light blocking layer are then, inparticular, oxides or nitrides or oxynitrides of Al, Ce, Ga, Hf, In, Mg,Nb, Rh, Sb, Si, Sn, Ta, Ti, Zn, Zr and the like.

The light blocking layer may be a metallic layer or a metallic layerstack. By way of example, the light blocking layer then comprises Tiand/or Cr or consists thereof. In this case, a thickness of the lightblocking layer is preferably at least 0.1 nm or at least 10 nm or atleast 50 nm and alternatively or additionally at most 10 μm or at most 2μm or at most 1 μm.

The light blocking layer may comprise a metallic layer or consistthereof, in particular as specified above. Optionally, an electricallyinsulating and/or dielectric intermediate layer is then situated at aside of the light blocking layer which faces the semiconductor layersequence. Leakage currents can be avoided or reduced by such anintermediate layer. Alternatively or additionally, an insulating and/ordielectric covering layer, for example, composed of an oxide or composedof a nitride, can be fitted at a side of the light blocking layer whichfaces away from the semiconductor layer sequence. Such a covering layermakes it possible to prevent the metallic light blocking layer frombeing wetted during soldering of the semiconductor laser and a solderfrom climbing up a facet. The in particular metallic light blockinglayer can therefore be embedded between two electrically insulatinglayers. The light blocking layer can directly touch one or both of theelectrically insulating layers.

The light blocking layer may be shaped from a semiconductor materialabsorbent for the laser radiation such as Si or Ge, or comprises such amaterial. The material can be doped to set the absorption properties.

An antireflection layer for the laser radiation generated in thesemiconductor layer sequence may be situated in places or over the wholearea at a side of the light blocking layer which faces away from thegrowth substrate. In other words, the light blocking layer is thensituated partly or completely between the antireflection layer and thegrowth substrate. The antireflection layer preferably covers the lightexit region.

The light blocking layer may be fitted in places or over the whole areaat a rear side lying opposite the front facet. In particular, the lightblocking layer may be fitted at the growth substrate at the rear side.Preferably, the light blocking layer at the rear side is formed from amaterial that is absorbent for the laser radiation or comprises such amaterial.

A highly reflective layer shaped as a resonator mirror for the laserradiation may be fitted in places or over the whole area at the rearside. It is possible for the light blocking layer to be situated at therear side in places or completely between the highly reflective layerand the growth substrate and/or the semiconductor layer sequence.

The semiconductor laser may comprise at least one monitor diode. Themonitor diode detects laser radiation generated in the semiconductorlayer sequence and can be used for power readjustment of thesemiconductor laser. The monitor diode is situated at the rear side ofthe growth substrate and is preferably designed to detect radiationemerging from the growth substrate.

Methods described here and optoelectronic semiconductor lasers describedhere are explained in greater detail below on the basis of examples withreference to the drawings. In this case, identical reference signsindicate identical elements in the individual drawings. In this case,however, relations to scale are not illustrated. Rather, individualelements may be illustrated with an exaggerated size to afford a betterunderstanding.

Turning now to the drawings, FIG. 1 shows an example of anoptoelectronic semiconductor component 1, which is preferably asemiconductor laser, in a perspective illustration. A semiconductorlayer sequence 2 comprising an active layer that generates a laserradiation is fitted on a substrate 3, which can be a growth substrate. Aplurality of bonding pads 10 are situated at a side of the semiconductorlayer sequence 2 which faces away from the growth substrate 3. Thebonding pads 10 make electrical contact with the semiconductor layersequence 2. The bonding pads 10 are preferably electrically drivableindependently of one another.

Individual layers of the semiconductor layer sequence 2 such as theactive layer or such as cladding layers, waveguide layers, barrierlayers, current spreading layers and/or current limiting layers are notdepicted in each case to simplify illustration.

During the operation of the semiconductor component 1, a laser radiationR is generated in the semiconductor layer sequence 2. The laserradiation R emerges at a front facet 4 of the growth substrate 3 and thesemiconductor layer sequence 2 in a light exit region 9. The light exitregion 9 comprises a region at the front facet 4 which preferablycorresponds to an exit area of the laser mode generated in thesemiconductor layer sequence 2. The light exit region 9 lies, inparticular, exactly opposite a required region of a resonator mirror ata rear side 12.

On account of spontaneous emission, on account of stray radiation and/orowing to an overlap of an electric field of the laser mode with thesubstrate, light outside the actual desired laser mode of the radiationR can pass into the growth substrate 3. This light is designated assubstrate mode S hereinafter. If the laser radiation R is blue or greenlight, then GaN, in particular, which is transparent to the radiation R,is used as growth substrate 3. It is thereby possible for radiation ofthe substrate mode S to propagate substantially in an unimpeded fashionin the growth substrate 3; also cf. FIG. 7.

The substrate mode S, in comparison with the actual laser radiation R,has a comparatively large area proportion at the front facet 4 of thegrowth substrate 3. In other words, the growth substrate 3 then itselfappears luminous and a beam quality is impaired on account of thesubstrate mode S. If the semiconductor laser 1 is used without furthermeasures, for example, in the context of a flying spot application forprojection, then a halo H can form around a projection region P, thehalo impairing an image quality. This is illustrated in FIG. 8.

To avoid such a halo H and prevent light of the substrate mode S frombeing emitted from the growth substrate 3, a light blocking layer 5 isfitted at the front facet 4. The light blocking layer 5 is at leastpartly opaque to radiation having a wavelength of the laser radiation R.In other words, the light blocking layer 5 prevents the substrate mode Sfrom leaving the growth substrate 3. The light blocking layer 5 is notapplied to the growth substrate 3 over the whole area.

In a departure therefrom, it is alternatively possible for the lightblocking layer 5 to cover the growth substrate 3 over the whole area atthe front facet 4. It is likewise possible for a part of thesemiconductor layer sequence 2 also to be covered by the light blockinglayer 5 at the front facet 4. By way of example, a distance between anactive zone of the semiconductor layer sequence 2 and the light blockinglayer 5, in a direction parallel to the growth direction G, is at least1 μm or at least 2 μm or at least 5 μm and alternatively or additionallyat most 70 μm or at most 20 μm or at most 10 μm. The fact of whether thesemiconductor layer sequence 2 is partly covered by the light blockinglayer 5 can therefore be dependent on a thickness of the semiconductorlayer sequence 2.

FIGS. 2A and 2B show examples of the semiconductor laser 1 in a planview of the front facet 4. The semiconductor laser 1 comprises a ridge20 of the semiconductor layer sequence 2 for impressing current and forguiding the radiation R. In other words, the semiconductor laser 1 isthen shaped as a ridge laser. Such lasers are also specified in US2003/0058910 A1, the subject matter of which is hereby incorporated byreference.

A distance d between the bonding pad 10 and the light blocking layer 5is approximately 5 μm, for example. In this case, it is not necessaryfor the light blocking layer 5 to have an exactly identical thickness oran exactly identical material composition over its entire extent, aslong as the light blocking layer 5 covers a sufficiently largeproportion of the front facet 4 and is opaque or substantially opaque towavelengths of the laser radiation 5 or has a sufficient absorption forsuch wavelengths. By way of example, in a manner governed by productionengineering, an edge of the front facet 4 is free of the light blockinglayer 5 all around, cf. FIG. 2B.

FIG. 3 illustrates a production method for the semiconductor component1. Dummy bars 6 and the growth substrates 3 with the semiconductor layersequences 2 and optionally the bonding pads 10 are arranged alternatelyin a rack 8. In this case, the dummy bars 6 project beyond the growthsubstrates 3 at the front facets 4 thereof.

The light blocking layer 5 applied to the front facets 4 is produced bya directional coating method. In this case, a coating is effected fromthe coating direction B. In a plane perpendicular to the front facets 4,an angle between the coating direction B and a growth direction G of thesemiconductor layer sequences 2 is less than 90° or less than 85°. As aresult, the front facets 4 near the semiconductor layer sequence 2 areshaded by the dummy bar 6 and the light blocking layer 5 is not appliedin this region; also see FIGS. 1 and 2.

Alternatively or additionally, there is another possibility forrealizing the shading during the production of the light blocking layer5, by a separate shadow mask situated between the growth substrates 3and a coating source.

In the method in accordance with FIG. 4, the dummy bars 6 each haveprojections 7 which, as seen in a plan view of the front facets 4, coverthe latter in a region near the semiconductor layer sequence 2. In thiscase, the projections 7 can be in contact with the front facet 4 orelse, preferably, be spaced apart from the front facet 4. In this case,the coating direction B can be oriented perpendicularly to the frontfacets 4 or else, as in FIG. 3, be oriented obliquely with respect tothe front facets 4.

In the example of the method in accordance with FIG. 5, the rack 8, atleast between the growth substrates 3, is free of dummy bars. The growthsubstrates 3 with the semiconductor layer sequences 2 and the optionalbonding pads 10 are arranged in a sawtooth-like fashion, as seen in sideview. In other words, the front facets 4 are in each case orientedparallel to one another, but offset relative to one another in adirection perpendicular to the front facets 4.

The growth substrate 3 which succeeds a growth substrate 3 along thegrowth direction G projects beyond the latter at the front facet 4 suchthat shading of the front facet 4 at the regions near the semiconductorlayer sequence 2 is ensured. In a plane perpendicular to the frontfacets 4, an angle between the coating direction B and the growthdirection G of the semiconductor layer sequences 2 is less than 90°.

In a departure from the illustration in accordance with FIG. 5, it isoptionally possible, in the same way as, for instance, in accordancewith FIG. 3 or 4, for dummy bars in each case to be situated betweenadjacent growth substrates 3 with the semiconductor layer sequences 2.

A conventional method is described in FIG. 6. In this case, the growthsubstrates 3 with the semiconductor layer sequences 2 are combinedalternately with dummy bars 6 to form a rack 8. The growth substrates 3with the front facets 4 project beyond the dummy bars 6. This ensuresthat the complete front facets 4 are coated. Therefore, partial regionsof the front facets 4 are not shaded by such a method. Regionallyapplying the light blocking layer, for instance, is not possible withsuch a method.

A further example of the method is illustrated schematically in FIG. 9.In accordance with FIG. 9, the dummy bars 6 are structured in a lateraldirection, that is to say in a direction in the plane of the drawing andperpendicular to the growth direction G. The dummy bars 6 have theprojections 7. The projections 7 shade only a small region at the frontfacets 4 all around the light exit region 9. As a result, in a lateraldirection only the ridge 20 and a small region of the semiconductorlayer sequence 2 and of the growth substrate 3 are not covered by thelight blocking layer 5.

Therefore, the light blocking layer 5 is also situated alongside thelight exit region 9 in places in a lateral direction. A distance betweenthe light blocking layer 5 and the ridge 20 all around is, for example,0.1 μm to 100 μM or 0.5 μm to 50 μm or 1 μm and 20 μm. In the example inaccordance with FIG. 9, the dummy bars 6 and the growth substrates 3 arepreferably arranged in the rack 8 analogously to the example inaccordance with FIG. 4.

FIG. 10A illustrates the light blocking layer 5 in greater detail. Inaccordance with FIG. 10A, the light blocking layer comprises two layerpairs of first partial layers 5 a and second partial layers 5 b. Thelight blocking layer 5 is shaped similarly to a Bragg mirror. Thepartial layers 5 a, 5 b preferably comprise materials having mutuallydifferent refractive indexes and each have a thickness of approximatelyλ/4, wherein λ denotes a principal wavelength of the laser radiation R.

By way of example the layers 5 a are produced from titanium dioxide, andthe layers 5 b from silicon dioxide. Alternatively, it is possible forone type of the partial layers to have a thickness of 0.2λ or 0.4λ andto be shaped from aluminum oxide, for example, and for the other type ofthe partial layers to have a thickness of 0.3λ or 0.6λ and to beproduced from hafnium oxide, for instance.

Preferably, either the first or the second partial layers are shapedwith a material absorbent to the laser radiation R, for example, fromsilicon or germanium, and the other partial layers are shaped from a lowrefractive index material such as silicon dioxide or aluminum oxide. Asa result, there is first a high reflectivity on account of thedifferences in refractive index between the layers and, secondly, thetransmission is significantly reduced on account of the absorption ofthe other partial layers.

In FIG. 10B, a transmission T in percent is plotted against thewavelength λ in nanometers for a light blocking layer 5 comprising fourlayer pairs each composed of λ/4 layers composed of aluminum oxide andsilicon, that is to say that the light blocking layer comprises a totalof eight partial layers. In the blue and in the green spectral range,the transmission T of such a light blocking layer 5 is below 1%. FIG.10C furthermore illustrates the dependence of the transmission T on thenumber N of mirror pairs. With just five mirror pairs, corresponding toten partial layers, the transmission at 450 nm is less than 10⁻⁴.

It is possible for such light blocking layers comprising partial layershaving a thickness of approximately λ/4 and comprising layers composedof a low refractive index material and a radiation-absorbing materialalso to be used in other optoelectronic semiconductor components such aslight emitting diodes, luminescence diodes or semiconductor lasersdifferent than those described here, such as surface emitting lasers,independently of the semiconductor components 1 described here.Preferably, such a light blocking layer then comprises one to five layerpairs and is produced from the materials specified above.

FIG. 11 illustrates a further example of the semiconductor laser 1 in aschematic side view. The light blocking layer 5 is fitted at the frontfacet 4 outside the light exit region 9, and likewise at the rear side12. The light blocking layer 5 comprises a material that is absorbentfor the laser radiation R. An antireflection layer 11 is applied overthe entire front facet 4, such that the light blocking layer 5 issituated between the growth substrate 3 and the antireflection layer 11.A highly reflective layer 13 is correspondingly applied over the entirerear side 12. By the highly reflective layer 13, a resonator mirror forthe laser radiation R is realized. With such absorbent light blockinglayers 5 at the rear side 12, too, substrate modes S can be suppressedparticularly efficiently.

In this case, antireflection layer can also mean that the layer 11 has alower reflectivity than the highly reflective layer 13. It is thenpossible for the layer 11 to be embodied as a resonator mirror for theradiation R. By way of example, the layer 11 in this case has areflectivity of 10% to 80% for the radiation R.

In the example in accordance with FIG. 12, the light blocking layer 5 isrealized by the highly reflective layer 13, which is also fitted at therear side 12. However, as seen in side view, the highly reflective layer13 at the rear side 12 covers only a region which lies opposite thelight exit region 9 and which is required to support the fundamentalmode of the laser radiation R. Remaining regions of the rear side 12 arecovered with the antireflection layer 11.

Furthermore, the semiconductor component 1 comprises a monitor diode 14fitted at the rear side 12 in the region of the antireflection layer 11.As a result, stray light passes from the growth substrate 3 through theantireflection layer 11 to the monitor diode 14. Consequently, a powerof the semiconductor laser 1 can be readjusted by stray light. Such amonitor diode makes it possible to regulate the power of thesemiconductor component 1 efficiently with the substrate mode S, withoutradiation R emitted at the front facet 4 having to be used for powerreadjustment.

In the case of the example in accordance with FIG. 13, no antireflectionlayer 11 is fitted at the rear side 12. The antireflection layer 11 atthe front facet 4 is applied continuously and over the whole area andthe light blocking layer 5 is situated at a side of the antireflectionlayer 11 which faces away from the growth substrate 3; also cf. FIG. 14.

Such highly reflective layers 13 and/or antireflection layers 11 canalso be present in all other examples of the optoelectronicsemiconductor component 1. A structuring of the antireflection layer 11and/or of the highly reflective layer 13 can be effected analogously tothe structuring of the light blocking layer 5 by directional coatingmethods in conjunction with shading.

In the case of such a configuration of the semiconductor laser 1, asillustrated in FIG. 14, by repeated reflective coating with layers 13and/or provision with antireflection layers 11, the reflectivity of thefront facet 4 and of the rear side 12 can be deliberately set locallydifferently such that the radiation R is coupled out efficiently at thefront facet 4, while the substrate mode S at the rear side 12 is guidedefficiently to the monitor diode 14.

In the case of the example of the production method in accordance withFIG. 15, the front facet 4 is produced by etching, for example, by dryetching. In other words, a part of the semiconductor layer sequence 2 isthen removed at least at the light exit side, see the sectionalillustration in accordance with FIG. 15A and the front view inaccordance with FIG. 15B. Alternatively, it is possible for the entiresemiconductor layer sequence 2 and a part of the growth substrate 3 tobe removed along the growth direction G to form the front facet 4, seeFIG. 15C. The projection 7 is therefore formed by the growth substrate 3itself. A length L of the projection 7, see FIG. 15A, is preferably atleast 0.1 μm and furthermore preferably at most 100 μm or at most 20 μmor at most 10 μm.

If the growth substrates 3 with the semiconductor layer sequences 2 arethen combined to form the rack 8, then the shading can be obtained bythe projection 7 during the production of the light blocking layer,which is not depicted in FIG. 15. The rack 8 can be free of dummy bars,see FIG. 15D, or else comprise the dummy bars 6, see FIG. 15E.

The methods, components and lasers described here are not restricted bythe description on the basis of the examples. Moreover, this disclosureencompasses any novel feature and also any combination of features,which in particular includes any combination of features in the appendedclaims, even if the feature or combination itself is not explicitlyspecified in the claims or examples.

The invention claimed is:
 1. An optoelectronic semiconductor lasercomprising: a growth substrate, a semiconductor layer sequence thatgenerates laser radiation, a front facet at the growth substrate and atthe semiconductor layer sequence which constitutes a main light exitside for the laser radiation generated in the semiconductor laser andhas a light exit region at the semiconductor layer sequence, a lightblocking layer for the laser radiation, which partly covers at least thegrowth substrate at the front facet such that the light exit region isnot covered by the light blocking layer, and a bonding pad at a side ofthe semiconductor layer sequence facing away from the growth substrate,wherein the light blocking layer comprises first and second partiallayers alternately succeeding one another, the partial layers, with atolerance of at most λ/7, have an optical thickness of λ/4, the firstand/or the second partial layers comprise a material that is absorbentfor laser radiation having the wavelength λ, the light blocking layercomprises 2 to 20 of the partial layers, and a distance between thebonding pad and the light blocking layer at least at the light exitregion is 0.1 μm to 100 μm.
 2. The optoelectronic semiconductor laseraccording to claim 1, wherein the light blocking layer comprises asemiconductor material having a band edge smaller than the wavelength λof the laser radiation, and/or wherein the light blocking layer isformed by a metallic layer or comprises such a layer.
 3. Theoptoelectronic semiconductor laser according to claim 1, wherein anantireflection layer for the laser radiation is applied at least inplaces at the front facet at a side of the light blocking layer facingaway from the growth substrate, and the antireflection layer covers thelight exit region.
 4. The optoelectronic semiconductor laser accordingto claim 1, wherein the light blocking layer is also fitted at least inplaces at a rear side lying opposite the front facet, and a highlyreflective layer as resonator mirror for the laser radiation is shapedat least in places at the rear side.
 5. The optoelectronic semiconductorlaser according to claim 1, wherein the highly reflective layer isapplied only in places at the rear side and a monitor diode for thelaser radiation is situated at the rear side.
 6. The laser according toclaim 1, wherein the light blocking layer comprises two to five pairs ofpartial layers.